Seasons• Understand how seasons work on the

Earth

• Literal world building of other planets

• Examples:– Indigenous religions, local calendars– Weather, planting seasons

• Bad example: “Winter is coming.”

Why you should care about wrong ideas

• Your preconceptions can cause inaccuracies in your writing

• Readers’ misconceptions can cause confusion when reading

• To accurately communicate, you need to know both the correct science and what your readers think

Answer the following questions privately to me using the colored cards

What season is it right now in Australia?

A. Spring

B. Summer

C. Fall

D. Winter

What causes the seasons on Earth?

A. Earth’s elliptical orbit causes it to sometimes be closer to the Sun

B. The tilt of the Earth’s axis causes more direct rays from the Sun

C. The tilt of the Earth’s axis causes parts of the Earth to be closer to the Sun

D. The tilt of the Earth’s axis changes so parts of the Earth are closer to the Sun

Popular Answer: A• The Earth’s orbit is elliptical. Seasons are

caused by the entire Earth’s distance from the Sun.

A Private Universe

• Harvard Smithsonian Center for Astrophysics (CfA), 1987

• http://www.youtube.com/watch?v=TrXaQu_qGeo

Popular Answer: A• The Earth’s orbit is elliptical. Seasons are

caused by the entire Earth’s distance from the Sun.

Problems with A• Whole Earth would experience the same

seasons at the same time

• How does this explain the length of the day?

• Why doesn’t the Sun look bigger in the Summer than the Winter?

http://www.definity-systems.net/~apw/astro/images/perihelion.jpg

What causes the seasons on Earth?

23.5º Tilt of Earth’s axis

2nd most Popular Answer: C

• Tilt of the Earth makes part of the Earth closer to the Sun and therefore warmer.

Problem with C

• Which part of the Earth is closer to the Sun?

Equator

23.5º Tilt of Earth’s axis alone

• Nothing to do with distance

• Directness of sunlight

• Length of day

• Path of Sun through the sky

Demos

• Seasons: – http://astro.unl.edu/classaction/animations/

coordsmotion/eclipticsimulator.html

• Rise/set of stars– http://astro.unl.edu/naap/motion2/

animations/ce_hc.html – “The Stars: A New Way to See Them” (by

H.A. Rey)

What causes the seasons on Earth?

A. Earth’s elliptical orbit causes it to sometimes be closer to the Sun

B. The tilt of the Earth’s axis causes more direct rays from the Sun

C. The tilt of the Earth’s axis causes parts of the Earth to be closer to the Sun

D. The tilt of the Earth’s axis changes so parts of the Earth are closer to the Sun

Imagine that the Earth was upright with no tilt. How would this affect the

seasons?

A. We would no longer experience a difference between the seasons.

B. We would still experience seasons, but the difference would be less noticeable.

C. We would still experience seasons, but the difference would be more noticeable.

D. We would continue to experience seasons in essentially the same way as we do now.

Bad Example:“Winter is coming.”

• In A Song of Ice and Fire (book series) and A Game of Thrones (TV series), Martin says Bran is 7 years old, and that he has not yet experienced winter.

• Huh? Martin doesn’t explain how years can be independent of seasons.

Possible Explanations of “Winter is coming.”

• Variable tilt?– Not likely due to stabilizing effect of having

a moon

• Elliptical orbit?– Not likely due to variable winter length and

decoupled year/seasons

• Circumbinary planet? – http://arxiv.org/pdf/1304.0445v1.pdf

• El Nino / Southern Oscillation?